Between 1986 and 1991, thyroidectomy was performed on 138 patients with hyperthyroidism. Thyroid carcinoma was found in eight patients (5.8 per cent). Eighty (58-0 per cent) of the 138 patients had toxic nodular goitre, 33 (23.9 per cent) toxic diffuse goitre and 25 (18.1 per cent) toxic adenoma. Concurrent carcinoma was more frequent in patients with toxic adenoma (8 per cent) than in those with Graves' disease (6 per cent) and toxic nodular goitre (5 per cent). Papillary carcinoma was found in seven patients and follicular carcinoma in one. Three papillary carcinomas were occult with a diameter less than 1.5 cm. Five patients received 100 mCi I-131 after operation. There was no morbidity. During follow-up of 10-45 months, there was neither death nor recurrence.